Data underlying the research of Mesophilic Fermentation Explorations for Anaerobic Carboxylates Production from Commercial Bioplastic Products: PHA-based ‘Happy Cups’ & PLA-based Lids

Biodegradable plastics such as polyhydroxyalkanoates (PHA) and polylactic acid (PLA) are increasingly applied in commercial products, but their end-of-life (EoL) processing remains inefficient in terms of carbon and energy recovery. Carboxylates, such as acetate and <em>n</em>-butyrate, are valuable platform chemicals that can serve as precursors for bioplastics, biofuels, and other biobased products. Producing carboxylates from biodegradable plastics offers a promising strategy to recover carbon and support circular EoL management beyond conventional options like composting or incineration. This study presents mesophilic open-culture fermentation strategies to convert commercial PHA and PLA raw materials and/or products into carboxylates. A sequential bioprocess was developed using a gas-lift anaerobic filter bioreactor, initiating in Phase I with batch fermentation of hydrolysates derived from hydrothermally pretreated PHA (10 g/L) and PLA (1.4 g/L) pellets. In Phase II, continuous operation produced 6.6 g/L acetate and 4.8 g/L <em>n</em>-butyrate from the same hydrolysates source. During Phase III, additional shredded commercial bioplastic products (PHA-based cups and PLA-based lids) were filled to co-ferment with hydrolysates, which further increased acetate and <em>n</em>-butyrate yields to 7.2 g/L and 5.5 g/L, respectively. In subsequent phases, hydrolysates feeding was stopped, and only the remaining solid bioplastics were used. The hydraulic retention time was extended from 2 to 18 days in Phase V. Overall, 35% of the PHA-based cups were converted into carboxylates, while PLA-based lids showed negligible degradation. Residual plastics were partially fragmented into microplastics. Microbial community analysis revealed that <em>Clostridium tyrobutyricum</em> likely played a key role in the hydrolysates fermentation of PHA and PLA pellets, while a broader microbial consortium contributed to solid bioplastic conversion.